Classifying liner for ball mills



Jan. 10, 1961 F. FALLA 2,967,671

CLASSIFYING LINER FOR BALL MILLS Filed June 26, 1958 4 Sheets-Sheet 1 'INVENTOR.

ff/WVAWDO 541m Jan. 10, 1961 F. FALLA CLASSIFYING LINER FUR BALL MILLS 4 Sheets-Sheet 2 Filed June 26, 1958 Jan. 10, 1961 r F. FALLA 2,967,671

CLASSIFYING LINER FOR BALL MILLS Filed June 26, 1958 4 Sheets-Sheet 3 INVENTOR. FEAA fl/VDO 5411/7 Byz r Jan. 10, 1961 F. FALLA 2,967,671

CLASSIFYING LINER FOR BALL MILLS Filed June 26, 1958 I 4 Sheets-Sheet 4 INVENTOR.

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CLASSIFYING LINER FOR BALL MILLS Fernando Falla, 59 Elm St., Millburn, NJ.

Filed June 26, 1958, Ser. No. 744,727

9 Claims. (Cl. 241-183) The invention relates, to a novel liner for the rotating cylinder of ball mills, more especially to a liner which will admit of satisfactory classification of the grinding media for the material to be comminuted within said cylinder, as well as of the material itself.

It has for an object to provide a novel construction of the ring elements forming the liner and to afford a novel arrangement of the same within the cylinder, whereby greatly to increase the efiiciency' of the grinding operation in securing a fine powder of the raw material, as for example, in the case of Portland cement, as Well as for use in the ceramic and mining industries.

Heretofore, the customary and most acceptable mills comprised a cylindrical shell adapted for the rotation, on. axially-extending tubular trunnions of relatively large diameter which admit the material, to be pulverized, at one end of said shell and discharge it at the other end. The interior of such cylindrical shell is, to this end, partly filled with balls of hard material but which is softer than the liner material. As the cylinder is designed to rotate at a velocity below the critical centrifugal speed of the balls, the latter are made to cascade on one another-the liner to this end being provided with horizontal vanes or grooves to prevent the ball charge from sliding on the surface of said liner.

For best results, the ball charge must be made up of balls of different diameters, the larger diameter balls serving to break the larger particles of the material to be ground and the smaller ones pulverizing the resulting particles of reduced size-said larger balls being caused to progress toward the feed end of the cylinder and the smaller ones toward the discharge end thereof.

As all of the balls become smaller in the course of the grinding, it is desirable that provision be made whereby they will be caused to accumulate at the discharge end of the mill for replacement by larger diameter balls. With the known type of ball mills such accumulation and replacement is not possible; and it is a further object of the invention to provide a liner which is constructed such that the balls, which have worn to a reduced size, will travel toward and accumulate at the discharge end of the mill.

A still further object of the invention is to provide a liner construction whereby a heavy accumulationofthe balls, may be avoided at both ends of the mill.

In the operation of grinding, two types of ball mills are generally utilized, viz: the overflow and theairswept; and the novel liner arrangement set' forth isparticularly applicable to both. Thus, in the case of the former type, the cavities provided in the novel liner blocks function to deliver the finer-particles to the discharge end of the mill, thereby expediting the pulverizing activity to clear faster the final pulverized material. With the air swept type .of ball mill, any residual finely pulverized rnateri'al in a cavity will be clearedinto-the-path of iair supply. throughthe mill to -enhance its efficiency.

States Patent The novel construction is particularly adapted toathe operation of extremely long ball mills which require ice design of the blocks of the ring liner elements eliminates the use of such partitions, as well as access doors to permit inspection and replacement of the proper size balls in the diiferent compartments.

In carrying out the invention, a succession of laterally contacting ring elements constitutes the liner for thein'ner surface of the ball mill cylinder, as is the general practice; but, in accordance with the invention, the inner surface of the respective ring elements is so modified as to isolate, when the cylinder is rotated, larger balls to the entrance portion of the mill and to clear small balls to the outlet end. Moreover, the construction is such that the material in process of grinding (smaller ground-up particles) is classified, viz: directed toward the discharge end of the mill for delivery. Pairs of surface pockets or cavities of differing diameters and depths are, to this end, provided in a raised, inclined surface of a block or blocks of which the ring elements are constituted; and the two pockets of a pair are arranged to merge with each other, as set forth. Moreover, surface grooves from the respective pockets serve as discharge channels for ternporarily retained balls. The top flat surface provided on a liner ring element, also, may be pitched downwardly in a direction opposite the rotation direction of the cylinder. Guide means are provided on a liner element in advance of said pockets to prevent balls already lodged therein from being struck.

The enhanced efiiciency of operation in utilizing the novel liner construction results in a material reduction in power consumption per ton of ground material; and a substantial cost reductionup to 30%--may be effected.

The nature of the invention, however, will best be understood when described in connection with the accompanying drawings, in which:

Fig. l is a longitudinal section through a ball mill equipped with the novel liner, and indicates also the drive mechanism for the same.

Fig. 2 is a transverse section through the mill taken on the line 2-2, Fig. l and looking in the direction of the arrows.

Fig. 3 is an isometric view of the block element of novel design and of which the ring liner elements are composed.

Figs. 4 and 5 are, respectively, a front view and a transverse section, taken on the line 55, Fig. 4, looking in the direction of the arrows, of said block element.

Fig. 6 is a longitudinal section through a ball mill equipped with the novel liner and Fig. 7 a fragmentary developed view illustrating a modification in the arrangement of the blocks making up a liner ring element.

Referring to the drawings, more particularly to Figs. 1 and 2 thereof, the ball mill comprises the conventional ball-retaining cylinder portion it) which is mounted for rotation on hollow end-bearings 11, 12, the former being designed to receive, through a feed spout 13 connected thereto, a charge of material to be crushed and ground in the mill. At the opposite and outlet end the comminuted product is designed to be discharged through a discharged spout 13' connected with the hollow end bear.- ing 12-in a manner well understood in the art.

Rotation of the cylinder 10 is conveniently effected grinding action as well as extending the useful life of r ball elements effecting the crushing and grinding of. the material fed into said cylinder. Said liner'to thisend comprises a plurality of ring elements 20 disposed adjafrom an electric motor 14 through intermediate gearing cently longitudinally of the cylinder 10 to fit tightly over its inner surface, each element consisting of a plurality of interlocking blocks 21 of conventional inner surface and one or more blocks 22 constructed in accordance with the invention. That is to say, reference being had to Figs. 3 to 5, the exposed working surface of a block 23 is of an undulating nature (Fig. but includes an intermediate plane surface portion 24 which is preferably pitched (as shown) in a direction opposite to the rotation direction of the cylinder 10.

The various ring elements may be assembled and fixed to the cylindrical shell 10, for example, by bolting the same thereto through intermediate wedges 25 included between a pair of blocks and nuts 26.

Balls 30, 31 for crushing and grinding purposes are indicated and their action is to be controlled in a novel manner, the direction of rotation of the cylinder being in accordance with the arrow indication, Fig. l.

The aforesaid plane surface 24 in accordance with the invention is recessed to afford two cylindrical and merging hemispherical cavities 32, 33 of different diameters, the former cavity 32 being the smaller and the depth of the same being greater than that of the cavity 33 of larger diameter. Furthermore, there extend outwardly from the respective cavities 32, 33 grooves 34 and 35 which diverge from each other in being directed oppositely to the cylinder rotation; and said grooves are designed to release balls of smaller size toward the discharge end of the mill and of larger size toward its feed end, respectively.

In addition, the leading wall of the intermediate plane surface portion 24 is provided with a wedge-shaped portion 36 lying in a plane perpendicular to the longitudinal axis of the cylinder and oppositely to the discharge grooves. The sides 37, 38 of said portion are differently sloped for the purpose of guiding some of the balls laterally in order to avoid collision with a ball already lodged in a cavity for classification.

Various combinations of the ring liner elements are possible depending on the size and type of material to be operated and also on the length of the mill cylinder over which the operation is conducted. Thus, as is indicated in Fig. 1 of the drawings, all of the classifying ring elements 20, with the exception of two at the respective ends which are provided with a single cavity 33 and 33" respectively, are provided with double cavitiesall sets being diametrically disposed and aligned longitudinally along a line parallel to the longitudinal axis of the cylinder.

The two end rings, however, are equipped with only the cavities of larger diameter in order to avoid a heavy accumulation of balls at the mill ends and to maintain a free inlet and outlet for the material to be pulverized and the pulverized material, respectively. It is also conducive to the maintenance of a higher ball level or charge within the mill with consequent increase in capacity.

In some instances, as with the pulverization from fines to super-fines, the end liners may be entirely free of cavities, particularly where the difference in ball sizes is not required to be large.

Instead of a single row only of the cavity pairs at diametrically opposite portions of the liner elements, several parallel rows 40, 41, 42 of the same may be provided along the succession of ring elements--reference being had to Fig. 7 of the drawings-with the pairs 40', l and 42; and in which case, every other ring along a row omits a pair, the pairs of adjacent rows thus being staggered relatively to each other.

In the case of a very long millsome mills being as much as 36 feet to 40 feet long-it will be advantageous to classify more than two sizes of the balls. In accordance with the invention, it is possible to maintain readily the proper size balls generally at the most suitable location and so increase the efficiency of the mill. In the present practice, mills of such length are equipped with perforated partitions in the attempt to retain the proper size balls in the selected compartment. This, however, does not prove successful since there is no way to keep the small balls in the final compartment, as well as larger balls, as they wear down, from jamming in the perforations of the partitions, which serve merely to prevent passage of large balls in the first compartment-the return of small balls thereto not being prevented.

Furthermore, to load the compartments it becomes necessary to shut down the mill to allow for opening of the compartment doors. This is not necessary with the novel combination set forth, in that replacement only of large balls at the feed end of the cylinder is required, together with the feed of material. The novel mill operates to classify automatically the balls which, when they become small enough and worn out will have been classified to the section selected by the liner elements in that section.

Referring to Fig. 6 of the drawings, the ball mill cylinder 45 is shown as having a number of the ring liner elements 46 at the feed end 47 of the mill free of cavities and discharge grooves, and similarly at the discharge end 48.

Moreover, provision is made with respect to the arrangement of cavities and discharge grooves over the remaining ring liner elements to classify three sizes of ballslarge, medium and small, the large balls 50 being classified toward the feed end by action of the cavities 51; the medium size balls 52 toward the intermediate portion of the mill by the action of the cavities 53, 54; and the smallest balls 55 toward the discharge end by the action of the cavities 56.

The operation of the novel classification arrangement is substantially as follows:

As the mill cylinder rotates with the standard ball charges, the balls keep on cascading into each other, as per level indicated in Fig. 1, because the speed of the mill is to be maintained slightly below the critical centrifugal speed of rotation which would keep the balls against the lining of said cylinder. In so doing, many balls work their way into the larger cavities. If the ball is large enough to fill such large cavity, it will remain there until the mill rotation gives the ball a position to cause it to fall off the liner by the action of gravity. At this moment, the ball cannot do anything but to follow the corresponding discharge groove which directs said ball to the feed end of the mill.

If a smaller ball works its way into the larger cavity it will automatically fall to the bottom of said cavity. It cannot, however, remain there if it is smaller than the associated smaller cavity because when the classifying portion of the liner is at the bottom of the mill, the ball will follow the corresponding groove to the bottom of the smaller cavity and be forced by the discharge channel toward the discharge end of the mill.

I claim:

1. A classifying liner for the rotating cylinder of ball mills comprising a succession of ring liner elements including a plurality of interlocking blocks having an inwardly directed undulating surface, and a selected block of a ring liner element being provided with a pair of merging hemispherical cavities of different diameters and respective integral discharge grooves, the said grooves diverging in a direction opposite to the cylinder rotation.

2. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein the respective cavities of a block are of different depths.

3. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein the depth of the cavity of lesser diameter is greater than that of the cavity of greater diameter.

4. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein a pair of diametrically oppositely-disposed blocks of a ring liner element are provided with the cavities and associated discharge grooves.

5. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein the cavities and discharge grooves of the ring liner elements adjoining the discharge end of the mill are of lesser diameter than the diameter of the cavities and discharge grooves of the liner elements adjoining the feed end of the cylinder.

6. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein a plurality of ring liner elements at the respective ends of the liner only are provided with a single cavity and corresponding discharge groove directed toward the middle of the mill.

7. A classifying liner for the rotating cylinder of ball mills according to claim 1, wherein the succession of ring liner elements are disposed adjacently longitudinally of said cylinder, and the selected ring element is provided with a plane portion having a pair of merging, ball-re ceiving cavities discharge grooves laterally and oppositely directed to the cylinder rotation.

8. A classifying liner for the rotating cylinder of ball mills according to claim 7, wherein the block of aselected ring liner element has an integral, wedge-shaped extension of the plane portion directed oppositely to the discharge grooves.

9. The classifying liner for the rotating cylinder of ball mills according to claim 8, wherein the inclined sides of the wedge-shaped extension are of different inclinations.

References Cited in the file of this patent UNITED STATES PATENTS 2,268,661 Kennedy Jan. 6, 1942 FOREIGN PATENTS 171,082 Austria Apr. 25, 1952 435,524 Germany Oct. 18, 1926 732,645 Germany Mar. 8, 1943 260,380 Switzerland July 16, 1949 

